C4 - chemical changes

• What is the pH scale range?

  0 to 14
• How can you measure the pH of a solution?

  Using pH indicators or pH meters
• What happens when acids and bases react?

  They neutralize each other
• What do strong acids produce in water?

  Protons (H+ ions)
• What is the difference between strong acids and weak acids?

  Strong acids release all H+ ions; weak acids do not
• What is pH a measure of?

  The concentration of hydrogen ions
• Why should strong acids not be confused with concentrated acids?

  Concentration refers to amount, not strength
• Name a strong acid.

  Hydrochloric acid
• If a student added strong acid to a weakly acidic solution of pH 6, what was the new pH?

  pH 3
• By how many times did the concentration of H+ increase when pH changed from 6 to 3?

  By 1000 times
• What are the reactions of acids with metal hydroxides and carbonates?

  • Acid + Metal Hydroxide → Salt + Water
  • Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
• How can you make soluble salts using an insoluble base?

  React the base with dilute acid
• How do you know when all the acid has been neutralized?

  The excess solid sinks to the bottom
• What should you do after neutralization to obtain the salt solution?

  Filter out the excess solid
• What is the process to obtain pure salt crystals from a solution?

  Evaporate some water and cool the solution
• What is the word equation for the reaction of calcium carbonate with hydrochloric acid?

  Calcium carbonate + Hydrochloric acid → Calcium chloride + Water + Carbon dioxide
• What is the balanced symbol equation for the reaction of sodium with water?

  2Na + 2H₂O → 2NaOH + H₂
• How do metals react with acids?

  They produce salt and hydrogen gas
• What does the reactivity of metals with acids indicate?

  It shows how well a metal reacts
• What happens when metals react with water?

  They form metal hydroxide and hydrogen
• Which metals react with water?

  Sodium, potassium, and calcium
• What is the general equation for the reaction of metals with water?

  Metal + Water → Metal Hydroxide + Hydrogen
• What is a redox reaction?

  It involves the transfer of electrons
• What does electrolysis mean?

  Splitting up with electricity
• What is produced during the electrolysis of molten ionic solids?

  Elements are formed
• What is the overall equation for the electrolysis of aluminium oxide?

  2Al₂O₃ → 4Al + 3O₂
• What happens during electrolysis of aqueous solutions?

  Water ions must be considered
• What is produced at the cathode during electrolysis of copper(II) chloride?

  Hydrogen gas is produced
• What is produced at the anode during electrolysis of copper(II) chloride?

  Chlorine gas is produced
• What are the tests for gases produced during electrolysis?

  • Hydrogen: "Squeaky pop" with a lighted splint
  • Chlorine: Bleaches damp litmus paper
  • Oxygen: Glowing splint burns more brightly
• What must be balanced in half equations during electrolysis?

  The number of electrons
• What is the ionic equation for the electrolysis of aqueous sodium chloride?

  2H⁺ + 2Cl⁻ → H₂ + Cl₂
• What happens when a halide is present in the solution during electrolysis?

  Halogens are formed at the anode
• What is produced at the anode during the electrolysis of copper bromide?

  Bromine gas is produced
• What is produced at the cathode during the electrolysis of copper bromide?

  Copper metal is produced
• How do metals vary in their reactivity?

  Some donate electrons more readily than others
• What is the reactivity series used for?

  • To compare the reactivity of metals
  • To predict reactions involving metals
• What happens when a more reactive metal displaces a less reactive metal?

  A more reactive metal kicks out the less reactive one
• What occurs when zinc is placed in copper sulfate solution?

  Copper forms on the lump of zinc
• Why do alkali metals react with water?

  They are more reactive than hydrogen